Australian victims are among 251 children who have been identified in a secret "members-only" child pornography website in the United States.

US authorities say they have arrested 14 men over the global child pornography ring.

Some of the men assumed female online personas to connect with the children - who ranged in age from three to 17 years old - on popular social networks.

The men were charged with conspiracy to operate a child exploitation enterprise.

Eleven of the men charged were from Louisiana and were running an underground website that had more than 27,000 subscribers.

US Homeland Security secretary Jeh Johnson said the men had no regard for their victims.

"[It was] one of the largest known online child exploitation operations in history," he said.

The victims have all been identified and contacted by authorities.

Most were in the US but two dozen were from other countries including Australia and New Zealand.

"Never before in the history of this agency have we identified and located this many minor victims in the course of a single child exploitation investigation," said Daniel Ragsdale, the Department of Immigration and Customs Enforcement (ICE) deputy director.

Online network concealed users' locations

The underground website was a hidden service board on the Tor network of Darknet, investigators said, referring to a hidden online network sometimes used for illicit activities.

The website shared videos of boys enticed into providing sexually explicit material through Tor, which allows online anonymity by routing internet traffic in a way that conceals a user's location, authorities said.